1. Field of the Invention
The present invention generally relates to optically pumped, solid-state, q-switched and linearly polarized laser cavity assemblies and, more specifically, to a method of combining these non-pump elements into a single component that can produce pulse energies of 1-1000 millijoules for military and commercial applications.
2. Description of Prior Art
Many military and commercial applications, require high power optical pulses. These, thus, normally employ lasers consisting of a cylindrical cavity assembly closely adjacent an energetic Xenon, pyrotechnic or similar type of flash lamp or diode Isaer that provides the necessary pump power. These pumps can include straight tubes or radiating surfaces as long as the cavity is and parallel to the optical or cylindrical axis, circular surfaces surrounding the cavity or spiral surfaces coaxial with the cavity. The cavity assembly for a high power pulsed laser as used in range-finders, i.e. all laser elements except the optical pump, is typically made up of at least four discrete elements. This application covers a three or more active element structure made into one component plus a base pallet. Applicants"" copending cases (NVL-3211) for a PSEUDO-MONOLITHIC Q-SWITCHED LASER WITH LINEAR POLARIZATION and Ser. No. 09/496,281 for a PSEUDO-MONOLITHIC Q-SWITCHED LASER WITH OPTICAL PARAMETRIC OSCILLATOR consist of two and three Components respectively plus a base pallet.
The first cavity element is a rod, many times longer than its diameter of nonconductive crystalline gain material that lases at a characteristic wavelength when exposed to radiation from the pump source. The rod normally has a uniform regular cross-section and a longitudinal optical axis centered in that cross-section. The ends of the rod are ground and polished normal to this axis and are usually coated with anti-reflection coatings to prevent reflection of light rays entering or leaving these ends parallel to this optical axis.
The second element is usually a perfectly flat highly reflective (HR) mirror, at least for the lasing wavelength, mounted precisely normal to the rod axis and spaced slightly from a first end of the rod. Thin film dielectric reflective filters have been used for this mirror to permit end pumping particularly in single mode lasers, but this technique is not as efficient for high power lasers as those mentioned above.
The third element is an output coupler or (OC) mirror which, though also highly reflective, has a specified percent transmission or leakage, at the lasing or output wavelength. This element is mounted similar to the second at the opposite or output end of the rod.
The fourth element is a passive q-switch, or a wafer of material with flat and parallel broad faces normally centered on the optical axis of the rod between the second and third elements. The passive q-switch reduces the Q of the high Q cavity defined by the other three elements, until the inverted population of energy quanta in the rod reaches a critical level. The wafer then automatically restores the high Q to generate a short high power pulse. The rod of gain material is usually a well known laser crystal, such as Neodymium:Yttrium-Aluminum-Garnet (Nd:YAG), ruby, etc. or it could be a glass, such as Erbium Glass (Er:Glass These laser materials absorb at the pump wavelength and fluoresce at lasing wavelengths. Certain types of material, such as Neodymium Vanodate (Nd:YVO4) emit linear polarized laser beams. However, this material is more expensive than Nd(YAG), is softer making it difficult to machine and does not themally match Nd The assembly will lase without the Q-switch, but does not emit sufficient peak power for range finders and similar applications. The q-switch concentrates the output photons in time spaced pulses that have peak powers several orders of magnitude greater than outputs that are not Q-switched. The passive q-switch can be a wafer of impregnated plastic or other materials.
The purpose of using adjustable spaced elements has been to compensate for their imperfect shape and/or placement. The disadvantage of these assemblies lies in the large number of elements required and the need for numerous adjustable support members that permit precise mechanical alignment of the various optical components. This approach makes manufacturing and repair of the assemblies very complicated and expensive.
A goal of the present invention is to reduce the number of parts in the cavity assembly to a single optical element to which may be added a novel base pallet to facilitate mounting to the flash lamp and other equipment associated with the range-finder. Linear polarization is also achieved without using special rod materials and may not even require additional active elements.
A photon pumped laser cavity assembly including a rod made from laser gain material with precisely polished sides and ends, on one end of which is permanently attached at least one wafer and/or a metallic reflective coating; the one wafer consisting of a Q-switch material with opposite broad surfaces ground precisely flat and parallel. The assembly may also include a second similarly ground wafer of polarizing material or a notch with precisely cut parallel opposed faces oriented at the Brewster angle to polarize the laser beam. The rod may further include a pallet or substrate with faces precisely aligned parallel to the rod""s optical axis.